1. Field of the Invention
The present invention relates to an innovative polyhydroxyalkanoate, particularly to a polyhydroxyalkanoate containing units each having on the side chain a substituted phenyl structure and a method of producing the same.
In addition, the present invention relates to a charge controlling agent for use in electrophotography, electrostatic recording, magnetic recording and the like, a toner binder, an electrostatic latent image developing toner, an image formation method using the toner, and an image forming apparatus for use therein.
2. Related Background Art
Polyhydroxyalkanoate (PHA)
Resins that can be decomposed with time by the action of microorganisms and the like, namely biodegradable resins are under development in terms of environmental protection, and for example, many types of microorganism have been reported to produce biodegradable resins having polyester structures (polyhydroxyalkanoate: hereinafter abbreviated as PHA) and accumulate the resin in the cell (Biodegradable Plastic Handbook, Biodegradable Plastic Research Associate, N.T.S. Co., Ltd., p. 178-197 (1995)).
These polymers such as PHA produced by microorganisms may be used for production of various kinds of products through melt processing as in the case of conventional plastics, and have biodegradability, namely an advantage that they are fully decomposed by microorganism in the natural environment. Therefore, for example, PHA produced by microorganisms never remains in the natural environment to cause contamination when it is disposed of, unlike many synthetic polymer compounds. In addition, in general, PHA produced by microorganisms is also excellent in biocompatibility, and is expected to be applied as medical flexible members and the like.
It is known that such PHA may have various compositions and structures depending on the type of microorganism to be used for the production of the PHA, the culture medium composition and the culture condition, and hitherto studies have been conducted mainly on control of the composition and structure of PHA to be produced in terms of improvements of properties of PHA.
[1] First, the biosynthesis of PHA obtained by polymerizing a monomer unit with a relatively simple structure such as 3-hydroxybutyric acid (hereinafter abbreviated as 3HB) is exemplified as follows:                (a) those containing 3HB and 3-hydroxyvaleric acid (hereinafter abbreviated as 3HV) (Japanese Patent Publication No. 6-15604, Japanese Patent Publication No. 7-14352, Japanese Patent Publication No. 8-19227 and Japanese Patent Application Laid-Open No. 5-7492);        (b) those containing 3HB and 3-hydroxyhexanoic acid (hereinafter abbreviated as 3HHx) (Japanese Patent Application Laid-Open No. 5-93049 and Japanese Patent Application Laid-Open No. 7-265065);        (c) those containing 3HB and 4-hydroxybutyric acid (hereinafter abbreviated as 4HB) (Japanese Patent Application Laid-Open No. 9-191893);        (d) those containing 3-hydroxyalkanoate having 6 to 12 carbon atoms (Japanese Patent No. 2642937); and        (e) biosynthesis using a single aliphatic acid as a carbon source (the resulting product is almost same as those of (d)) (Appl. Environ. Microbiol, 58(2), 746 (1992)).        
They are all PHA composed of monomer units each having an alkyl group in the side chain, synthesized by β-oxidation of hydrocarbons and the like or synthesis of fatty acids from saccharides by microorganism, namely “usual PHA”.
Such PHA has already found considerable applications with proven performance particularly Also, in the field of agriculture, the biodegradable resin is used in mulch files, horticulture materials, slow-releasable agricultural chemicals, fertilizers and the like. Also, in the leisure industry, the biodegradable resin is used in fishing lines, fishing tackles, golf requites and the like.
However, if considering a wide range of application as a plastic, it cannot be the above described that PHA is fully usable in terms of properties in the present situation. For further expanding the range of application of PHA, it is important to conduct a wide range of studies on the improvement of properties, and for this purpose, development and search of PHA including monomer units of a variety of structures is prerequisite.
On the other hand, PHA with a substituent group introduced in the side chain (“unusual PHA”) can be expected to be developed as a “functional polymer” with very useful functions and properties originating from the introduced substituent group by selecting the introduced substituent group according to desired characteristics and the like. That is, it is also an important challenge to conduct of development and search of excellent PHA enabling such functionality and biodegradability to be compatible with each other.
[2] Examples of substituent groups include groups containing aromatic rings (phenyl group, phenoxy group, etc.), unsaturated hydrocarbons, ester groups, allyl groups, cyano groups, halogenated hydrocarbons and epoxide. Among them, studies on PHA having an aromatic ring are particularly vigorously conducted.                (a) PHA containing a phenyl group or its partially substituted group        
It is reported that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-phenylvaleric acid as a unit using 5-phenylvaleric acid as a substrate in Markromol. Chem., 191, 1957-1965 (1990) and Macromolecules, 24, 5256-5260 (1991).
It is reported that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(4′-tolyl)valeric acid as a unit using 5-(4′-tolyl) valeric acid as a substrate in Macromolecules, 29, 1762-1766 (1996).
It is reported that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(2′,4′-dinitrophenyl)valeric acid and 3-hydroxy-5-(4′-nitrophenyl)valeric acid as a unit using 5-(2′,4′-dinitrophenyl)valeric acid as a substrate in Macromolecules, 32, 2889-2895 (1999).                (b) PHA containing a phenoxy group or its partially substituted group        
It is reported that Pseudomonas oleovorans produces a PHA copolymer of 3-hydroxy-5-phenoxyvaleric acid and 3-hydroxy-9-phenoxynonanoic acid using 11-pheoxyundecanoic acid as a substrate in Macromol. Chem. Phys., 195, 1665-1672 (1994).
Japanese Patent No. 2989175 discloses a homopolymer consisting of 3-hydroxy-5-(monofluorophenoxy)pentanoate (3H5(MFP)P) units or 3-hydroxy-5-(difluorophenoxyl)pentanoate (3H5(DFP)P) units, a copolymer containing at least (3H5(MFP)P) units or (3H5(DFP)P) units; Pseudomonas putida synthesizing these polymers; and a method of producing the above described polymers using Pseudomonas species, and it is described that as an advantage of the above invention, a long chain aliphatic acid having substituent groups can be metabolized to synthesize a polymer having a phenoxy group substituted with 1 or 2 fluorine atoms at the side chain terminal, and stereoregularity and water repellency are provided while maintaining a high melting point and good processability.
Studies are conducted on cyano-substituents and nitro-substituents in addition to the fluorine-substituent described above.
In Can. J. Microbiol, 41, 32-43 (1995) and Polymer International, 39, 205-213 (1996), it is reported that PHA containing 3-hydroxy-p-cyanophenoxyhexanoic acid or 3-hydroxy-p-nitrophenoxyhexanoic acid as a monomer unit is produced with octanoic acid and p-cyanophenoxyhexanoic acid or p-nitrophenoxyhexanoic acid as substrates using a Pseudomonas oleovorans ATCC 29347 strain and a Pseudomonas putida KT 2442 strain.
These reports are useful in obtaining polymers each having an aromatic ring in the side chain of PHA and having properties derived therefrom unlike general PHA whose side chain contains an alkyl group. That is, such PHA containing units each having an aromatic ring having a substituent group on the ring is a multifunctional PHA given an additional function derived from the substituent group existing on the aromatic ring while maintaining polymeric characteristics of high melting point and good processability derived from the aromatic ring.
[3] In addition, on the other hand, studies are vigorously conducted for the purpose of obtaining multifunctional PHA by introducing an optional functional group in the polymer side chain a chemical reaction using a vinyl group for a produced polymer, based on PHA having the vinyl group in the unit.
It is reported in Polymer, 41, 1703-1709 (2000) that a change of solubility in solvents has been found such that 3-hydroxyalkanoic acid having diol on the side chain terminal, synthesized by an oxidation reaction using potassium permanganate after producing PHA containing as a monomer unit 3-hydroxyalkenoic acid having an unsaturated bond in the terminal of the side chain terminal using 10-undecenoic acid as a substrate, is rendered soluble in polar solvents such as methanol, acetone-water mixture (80/20, v/v) and dimethylsulfoxide, and insoluble in nonpolar solvents such as chloroform, tetrahydrofuran and acetone.
It is reported in Macromolecular chemistry, 4, 289-293 (2001) that an improvement in speed of decomposition has been found for PHA containing 3-hydroxy-9-carboxynonanoic acid as a monomer unit, synthesized by an oxidization cleavage reaction using potassium permanganate after producing PHA containing as a monomer unit 3-hydroxy-10-undecenoic acid using 10-undecenoic acid as a substrate.
It is reported in Macromolecules, 31, 1480-1486 (1998) that a polyester having an epoxy group on the side chain has been obtained by producing a polyester having a vinyl group on the side chain by means of Pseudomonas olevorans and then epoxidizing the vinyl group.
A report on a crosslinking reaction carried out by heating together with hexamethylene diamine a polymer having an epoxy group on the side chain, obtained in the same manner, and the analysis of the product from the reaction is provided in Polymer, 40, 3787-3793 (1999).
A report on a research achieving improvements of properties of polyester by making a crosslinking reaction proceed in polyester molecules using the vinyl group on the polyester side chain is provided in Polymer, 35, 2090-2097 (1994).
As shown from the researches described above, the vinyl group exhibits high reactivity in an addition reaction or crosslinking reaction.
On the other hand, a polymer having an aromatic ring on the side chain has thermal stability, and therefore introduction of the vinyl group being an active group capable of enduring various applications in units constituting PHA together with the aromatic ring can be expected to improve the thermal stability, and thus can be very useful in terms of application of polymers as functional materials.
General Technical Background of Toner
So far, many methods have been known for electrophotography, and those methods are generally carried out in such a manner that an electric latent image is formed on an image carrier (photoconductor) by a variety of means using a photoconductive substance, the latent image is then developed with a toner to form a visible image, and the toner image is transferred onto an object transfer material such as a paper as necessary, followed by fixing the toner image on the object transfer material by heat and/or pressure or the like to obtain a copy. For the method for visualizing the electric latent image, a cascade development method, a magnetic brush development method, a pressurizing development method and the like are known. Further, a method using a magnetic toner and a rotary development sleeve with a magnetic pole placed at the center thereof in which the magnetic toner is caused to fly from the development sleeve onto the photoconductor by a magnetic field is also used.
Development systems for use in development of an electrostatic latent image include a two-component development system using a two-component type developer constituted by a toner and a carrier, and a one-component development system using a one-component type developer constituted only by a toner and using no carrier.
Here, the coloring fine particle generally called as a toner has a binder resin and a coloring material as essential components, and in addition thereto, magnetic powders and the like as necessary. For the method for imparting an electric charge to the toner, the electrifiability of the binder resin itself may be used without using a charge controlling agent, but in this method, charge stability with time and humidity resistance are compromised, thus making it impossible to obtain high quality images. Therefore, the charge controlling agent is usually added for the purpose of maintaining and controlling the charge of the toner.
Charge controlling agents well known in the art today include, for example, azo dye metal complexes, aromatic dicarboxylic acid-metal complexes and salicylic acid derivative-metal complexes as negative friction charging agents. In addition, as positive friction charging agents, nigrosine-based dyes, triphenylmethane-based dyes, various types of quaternary ammonium salts and organic tin compounds such as dibutyl tin oxide are known, but toners containing these substances as the charge controlling agent do not necessarily fully satisfy quality characteristics required for the toner such as the electrifiability and stability with time depending on their compositions.
For example, a toner containing an azo dye metal complex known as a negative charge controlling agent has an acceptable charge level, but may have reduced dispersibility depending on the type of binder resin to be combined because the azo dye metal complex is a low-molecular crystal. In this case, the negative charge controlling agent is not uniformly distributed in the binder resin, the charge level distribution of the obtained toner is significantly lacking in sharpness, and the obtained image has a low gray-level, resulting in a poor image formation capability. In addition, the azo dye metal complex has a unique color tone, and is thus presently used only for toners having limited colors around black, and if the azo dye metal complex is used as a color toner, its lack in clarity as a coloring agent required for obtaining an image having a high level of requirement for the color tone is a serious problem.
In addition, examples of almost colorless negative charge controlling agents include aromatic dicarboxylic-acid metal complexes, but they may be disadvantageous due to the fact that they are not perfectly colorless, and that they have low dispersibility peculiar to low-molecular-weight crystals.
On the other hand, nigrosine based dyes and triphenylmethane based dyes are presently used only for toners having limited colors around black because they are colored themselves, and may be poor in time stability of toners for continuous copying. In addition, conventional quaternary ammonium salts may have insufficient humidity resistance when formed into toners, and in this case, the stability with time may be so poor that high quality images are not provided as they are repeatedly used.
In addition, in recent years, attention has been given worldwide to reduction of wastes and improvement of safety of wastes in terms of environmental protection. This problem applies to the field of electrophotography as well. That is, as imaging apparatuses have been widely used, the amounts of wastes of printed papers, discarded toners and copying papers have increased year by year, and the safety of such wastes is important from a viewpoint of protection of global environment.
Application of Biodegradable Resin to Toner Application of a biodegradable resin to a binder resin particularly in production of toners is proposed in the field of electrophotography as well. For example, U.S. Pat. No. 5,004,664 discloses a toner having as its composition a biodegradable resin, particularly polyhydroxy butyric acid and polyhydroxy valeric acid, a copolymer thereof or a blend thereof. In addition, Japanese Patent Application Laid-Open No. 6-289644 discloses an electrophotographic toner particularly for heated roll fixation characterized in that at least the binder resin contains a plant based wax and a biodegradable resin (e.g. polyester produced by microorganism, and natural polymer material of plant or animal origin), and the above described plant based wax is added in the above described binder in an amount of 5 to 50% by weight.
In addition, Japanese Patent Application Laid-Open No. 7-120975 discloses an electrophotographic toner characterized by containing a lactic acid based resin as a binder resin. In addition, Japanese Patent Application Laid-Open No. 9-274335 discloses an electrostatic latent image developing toner characterized by containing a polyester resin obtained by dehydrating polycondensation of a composition containing lactic acid and tri- or higher functional oxycarboxylic acid and a coloring agent.
In addition, Japanese Patent Application Laid-Open No. 8-262796 discloses an electrophotographic toner containing a binder resin and a coloring agent, characterized in that the binder resin is composed of a biodegradable resin (e.g. aliphatic polyester resin), and the coloring agent is composed of non-water soluble pigments. In addition, Japanese Patent Application Laid-Open No. 9-281746 discloses an electrostatic latent image developing toner characterized by containing an urethane-modified polyester resin obtained by cross-linking polylactic acid with a tri- or higher functional polyvalent isocyanate and a coloring agent.
Any one of the above described electrophotographic toners contains a biodegradable resin as binder resin, and is regarded to be effective to contribute to preservation of environments and the like.
However, reports of examples of using a biodegradable resin in the charge controlling agent have not been known, and there is a room for further improvement for contribution to preservation of environments.
A polyester obtained by subjecting to a chemical reaction/treatment a polyester having the vinyl group reported so far can be given a variety of functions, but does not necessarily have satisfactory thermal characteristics because of the existence of a middle to long alkyl chain in the side chain. That is, the glass transition temperature and melting point of the polyester is low, resulting in significant limitations to the range of applications as moldings and films.
On the other hand, a polyester having an aromatic ring on the side chain generally has a high melting point and thus finds a wide range of applications as moldings and films as described previously. However, the polyhydroxyalkanoate having units each containing an aromatic ring substituted with a functional group capable of enduring a variety of applications includes only examples described above, and further more functional polyhydroxyalkanoates have been desired.
In addition, for solving the above described problems, the present invention provides a negatively charged charge controlling agent being more contributable to preservation of environments and the like, and having high performance (high charge level, quick start of charge, excellent stability with time, and high environmental stability) and improved dispersibility in the aspect of functionality, a toner binder containing the charge controlling agent, an electrostatic latent image developing toner containing the charge controlling agent, and an image formation method and an image forming apparatus using the electrostatic latent image developing toner.
For solving the above problems, the inventors have vigorously conducted studies, and found that a polyhydroxyalkanoate having units each containing an aromatic ring substituted with a functional group capable of enduring a variety of applications can be prepared by making a polyhydroxyalkanoate containing units each having a vinyl phenyl structure react with a compound having desired functional groups.
In addition, the inventors have found that the above polyhydroxyalkanoate has excellent characteristics as a charge controlling agent, and has a high level of safety for human bodies and environments, and that a significant effect can be exhibited when an electrostatic latent image developing toner containing the charge controlling agent and the electrostatic latent image developing toner are used in an image forming apparatus having a certain development system.
That is, the present invention relates to an innovative polyhydroxyalkanoate (PHA) containing units each having a substituted phenyl structure on the side chain and a method of producing the same. More particularly, the present invention relates to a method of producing the polyester using, as a raw material, PHA containing 3-hydroxy-ω-(4-vinylphenyl) alkanoic acid units.
In addition, the present invention relates to a charge controlling agent for use in electrophotography, electrostatic recording, magnetic recording and the like, a toner binder, an electrostatic latent image developing toner, an image formation method using the toner, and an image forming apparatus for use therein. Particularly, the present invention relates to a charge controlling agent for use in electrophotography, electrostatic recording and electrostatic printing in a copying apparatus, a printer, a facsimile machine and the like for forming an image in such a manner that a toner image is previously formed on an electrostatic latent image carrier (hereinafter, referred to simply as image carrier) and thereafter the image is transferred onto an object transfer material, a toner binder, an electrostatic latent image developing toner, an image formation method using the toner and an image forming apparatus for use therein. More particularly, the present invention relates to a negatively charged charge controlling agent safer for the human body/environment, a toner binder using the agent, an electrostatic latent image developing toner, an image formation method using the toner, and an image forming apparatus for use therein.